How did i turn my auto into full time four?

The real question is who let this guy (me) do a conversion? First let me preface all with the fact that I have recently quit chewing. That is a good excuse for my recent lack of mechanical oversight; right? Well, in searching for bad vibrations I was playing with truck in gear vs. out of gear tonight. Bad vibration in gear, not so much out of gear. Ok I block her up, slam on the e brake, put her in gear and crawl under. To my suprise the front drive shaft is spinning (hubs out). That is funny I swore i was in 2 high. Ok I will check and for good measure put t case in neutral (vibration gone) front driveshaft still spinning. Well long story short I must have my linkage messed up. Please feel free to mock, poke fun, chortle, laugh hysterically, or give me your deepest sympathy. Please tell me how to shift t case without the linkage hooked up. Where is neutral? Where is an extra 50K so I can go buy one with a warranty and then trade it in at 60k miles so I never even have to service it, because obviously I am too dumb to do anything but drive it, all the while not knowing there is a t case or such a thing as transmission oil?

Ok I won't laugh but have to ask if you checked this when you were under truck you said front shaft was spinning ? but was it spinning with force or just free wheeling ? our truck's I believe do allow the front shaft to spin but it's not forcefull .

I was going to get in here and get rid of all that I said, but you guys already replied. Yeah, it was freewheeling. All right, how do I trouble shoot this last vibration. With t-case in neutral i have no vibration. T case in gear i have vibration with trans in gear (no vibration in park or neutral). I quieted down the exhaust too, I tightened up the clamp bolted up to the hanger on the bell housing. I put a bit of a crimp in the down pipe but exhaust i think sounds good now.